Safety-connection



(No Model.)

E. THOMSON.

' SAFETY GONNEGTION- No. 426,082. Patented Apr. 22,- 1890.

INVENTOR 1 Elzhu, Thorn/Yon,

A TTORNEY.

UNITED STATES PATENT OFFICE.

ELIHU THOMSON, OF LYNN, MASSACHUSETTS.

SAFETY-CONNECTION.

I SPECIFICATION forming part of Letters Patent No. 426,082, dated April 22, 1890.

Original application filed October 8, 1888. Serial No. 287,56 i. Divided and this application filed August 5, 1889. Serial No. 319,834. (No model.)

To all whom it may concern:

Be it known that I, ELIHU THOMSON, a citizen of the United States, and a resident of Lynn, in the county of Essex and State of Massachusetts, have invented certain new and useful Safetyflonnection s, of which thcfollowing is a specification.

In the operation of electric circuits carrying currents of high tension a source of danger arises from the fact that a neighboring local circuit or conductor or conducting material may become accident-ally connected with the high-tension circuit. Under this con I dition a person Whose body forms a groundconnection from the local circuit or conductor may receive a dangerous shock, if at the same time there be a distant ground upon the main or high-tension circuit. This danger is present in greater or less degree whether the neighboring conductor be carrying an electric current or not; and it is the object of my invention to provide for any condition, where from the location or nature of the neighboring conductor, it may acquire accidentally, for the time being, the tension of a high-tension circuit, and so may become a source of danger to a person touching the same.

My invention, while applicable to many cases, is especially designed for application to systems of electric distribution in which the local or neighboring circuit is the path of currents derived, abstracted, or converted from the main, but of lower tension, a wellknown example of such system being the alternating-current system. of distribution by induction-coils or converters. Other systems are referred to in my prior patent, No. 322,138.

My present imvention relates to the use of the safety or low-resistance shunt or connection to earth, such as that described in my prior patent, No. 322,138, the arrangement being such in the present case that normally there is no connection to ground from the secondary or local circuit until a connection is formed between the primary and secondary, whereby the high potential of the primary or main line is transferred to the secondary or local circuit or apparatus.

My present invention consists, essentially,

in the provision of an insulating-film some where in the safety or shunting ground-wire, which insulating-film norm ally separates orinsulates two contacts or electrodes, but 011 being punctured, pierced, disrupted, or otherwise affected by the high-tension current leaking to the secondary or local will permit or cause electrical connection to be formed between such contacts by arcing and melting of the metal, transfer of metal, impingement of one contact upon the other through spring or other pressure, reduction of the 'l'llm from an insulating to a conducting state, or by any other action whereby two contacts normally insulated by a very narrow space may have electric connection established between them.

My invention consists, also, in the combination, with the device, of a condenser applied in the manner and for the purpose hereinafter set forth.

In the accompanying drawings, Figure 1 illustrates diagrammatically the application of my invention to the secondary circuit of a transformer. Fig. 3 illustrates a modification. Fig. 2 shows the manner of applying a condenser.

Thus in Fig. 1 a and 1) indicate a high potential primary line, a branch from which passes through a primary coil P in the ordinary way wound for high potential, and which is the primary of an induction-coil. The secondary S of the same coil, wound parallel to the coil P, is used to feed a consumption-circuit of lights L L, or other devices in the usual manner, suitable fuses being provided in both primary and secondary circuits fff f. From some point in the secondary circuit, preferably near the middle, a connection is taken to a contact-piece K, bearing on a film or a thin layer of insulating material F, of oiled paper or of other material, and with an earth plate or connection G on the other side of the film, forming, as it were, a film cut-out or weak spot in the insulation between the earth or ground and the secondary circuit. Instead of paper, any other insulating material may be employed, such as that hereinafter described. So long now as no connection whatever exists between the primary coil or circuit P receiving high-potential discharges and the secondary coil or circuit S in which low-potential currents are induced there will be no discharge tending to puncture or force its way through the film F. If, however, a connection, either temporary or permanent, is formed between the circuit a Z) or primary coil P and the secondary .coil 8 or other conductor, such that the potential of the primary line or other conductor is taken up by the secondary, the film F is punctured by the endeavor of the high-potential current to leak to ground, provided, of course,

that anywhere on the primary circuit a b a su ificient leakage or static inductional capacity tendency exists to give rise to the necessary discharge to earth in puncturing the film. It is needless to say that such leak or static inductional capacity is usually found in a circuit of considerable length.

hen the film has been punctured, a direct connection is established between the contacts or electrodes K G, one or both of which may be spring-pressed in the manner indi cated. The conductor or secondary coil S is then solidly connected to earth by a circuit of low resistance, and no danger can exist in touching the wires of the secondary circuit, even though connected with the primary circuit, when a person may be at the same timegrounded, for he is already shunted by the connection through the electrodes K G to earth. After the film is punctured the de vice becomes the same in essence as that de scribed in my former patent.

In my present invention the low resistance grounding of the secondary or other conductor to earth does not occur until the secondary has reached the same potential, or as large a part of the potential of the primary, when an instantaneous puncturing of the film F takes place.

It may be well in some cases to shunt the film, as it were, or, rather, to place around the film a condenser, as in Fig. 2, of small capacity, the condenser being represented at O, and consisting of plates separated by insulating material in the ordinary way, the plates opposed to each other being respectively connected one to the ground-circuit and the other with the connection to the coil 8 or septum near it. In this case a small amount of static induction or leakage may occur between the primary and the secondary without forcing the puncturing of the film F, and the formation of a good connection between the metal pieces normally separated by said film, the condenser C acting to remove the current which would reach the secondary by such small or slight induction or leakage; but if a solid connection between the primary coil P and the secondary coil 8 be formed, then the condenser O is insufficient in capacity to condense or lower the potential of the alternating discharges which reach the secondary and the film is at once punctured, making the connection to earth as before and shunting the condenser. The lines L L themselves might have a similar connection, as indicated by the dotted lines 10, Fig. 1.

In my former patent I have shown the safety ground wire or circuit as leading from a conducting-septum interposed between the primary or main and the secondary or local circuit, and which septum assumes or partakes of the dangerous potential of the secondary or local circuit whenever the latter becomes connected with the main or prinei pal circuit carrying the current of high tension by any discharge tending to pass from the high potential primary to the secondary. The sheath or septum is placed between the primary and the secondary coils wherever they are opposed or wherever they are capable of having a connection formed between them, either directly or through the iron core itself of the induction-coil, the. The application of my present invention to this modi fication is shown in Fig. 3, where I indicates the interposed conductor between the primary and secondary.

I do not claim in this application the broad invention of keeping the safety ground-connection of my prior patent normally open and establishing it through the agency of the highpotential current, which forces its way to ground whenever the local and the high-potential cireuitsbeeome accidentally connected, as this invention forms the subject of my prior application for patent filed October 8, 1888, No. 287,564, of which the present application is a division.

It is obvious that my present invention is applicable to any circuit or conductor whatever which is liable to dangerous connection with a high-potential circuit carrying currents of great tension, and will form an 0theicnt protection when the film or layer of illsulating material is not of too great thickness or too difiicult to puncture.

I have specified the use of a film of paper as the insulating material; but instead of paper some material. which is normally an insulator, but which by the action of the current will be reduced to a conducting state, maybe employed. For this purpose a thin layer of oxide of lead might be applied as a paste to one of the contacts or electrodes. This material is normally an insulator. IVhen the hi ghpotential current breaks its way through the thin film, it generates heat, which reduces the lead to a conducting state and forms or aids in forming the electrical connection between the two electrodes.

The following combinations of devices I do not claim herein, as they form the subject of claims in my application for patent filed J an nary 29, 1890, Serial No. 338,528, filed as a division of my original application filed October 8, 1888, Serial No. 287,564

1. The combination, with a transformer, of a ground branch from the secondary thereof normally interrupted by an insulatingspace, as and for the purpose described.

2. The combination, with a transformer, of a safety-fuse in the circuit thereof and a ground branch from the secondary circuit con taining electrodes normally separated from one another by a narrow insulating-space.

3. The combination, with a local circuit having fuses in each pole between the translating devices and the source, of a ground-circuit from each pole, including electrodes normally separated from one another, but adapted to form a path forahigh-tension current passing from one to the other, as and for the purpose described.

. \Vhat I claim as my invention is- 1. The combination, with a local or independent circuit or conductor liable to accidental. connection with ahigh-tension conductor, of a safety ground-connection formed by wires or conductors adapted to carry the current of the high-tension circuit without interruption, such safety ground-connection having interposed in it two contacts or electrodes separated from one another by a narrow insulating-film, across which the high-tension current may force its way.

2 In a system of electrical distribution in which local lines are supplied with currents of low tension from a high-potential line, the combination,with such local line, of a low-resistance ground wire or circuit normally interrupted by an insulating-film interposed between two contacts or electrodes placed in close proximity and adapted to be united to one another to complete the low-resistance ground-circuit, and wires or connections from said contacts or electrodes to ground and to the local, said wires or connections being adapted to carry without interruption the current flowing over such ground wire or circuit when completed over the said contacts or electrodes.

3. The combination, with a film cut-out or automatic connector, consisting of electrodes bearing one upon the other, but normally separated by insulating material, of a condenser in ashunt around said electrodes.

4. The combination, with an electric con- Verter, of a ground from the secondary thereof, including electrodes, between which is a thin layer ofi insulating medium, and a condenser in a shunt around said electrodes, as and for the purpose described.

5. The combination, with a high-tension circuit and a low-tension local circuit supplied with current by conversion from the first, of connections from the two sides or poles of said local circuit to separate electrodes normally separated by a thin insulating medium from electrodes connected severally to earth, each pair of electrodes being constructed and arranged, as described, so as to be electrically connected by the hightension current which forces its way across the narrow insulating space between them.

6. The combination, with electrodes separated by a thin layer of some insulating medium and placed in a ground-connection from a conductor liable .to accidental connection with a high-tension circuit or conductor, of a condenser in a branch or shunt around said electrodes. I

'7. The combination,with an electric conductor liable to accidental connection with a high-tension conductor, of a safety ground connection or protector, consisting of two contacts or electrodes having a bias toward one another, but separated normally by a thin layer of insulating material, said electrodes having connections to earth and to the circuit to be protected, adapted to carry the current flowing across the electrodes without interruption, as and for the purpose described.

Signed at Lynn, in the county of Essex and State 0t Massachusetts, this 1st day of August, A. D. 1889.

ELIHU THOMSON.

Witnesse JOHN W. -GIBBONEY', A. L. RoHRuR. 

